1. Field of the Invention
The present invention relates to an electric vacuum cleaner and, more particularly, to an electric vacuum cleaner in which the input to an electric blower is automatically controlled in accordance with the conditions of floor surfaces.
2. Description of the Background Art
Conventionally, a technique was proposed for improving the convenience of use of an electric vacuum cleaner by changing the input to an electric blower, i.e. the supply of power, in accordance with the magnitude of the load of suction and the amount of duct collected in a dust collecting chamber. Such a conventional technique as proposed includes a pressure detecting device provided in an air inlet passage between an electric blower and a filter. The pressure in the dust collecting chamber is detected by the pressure detecting device, and input to the electric blower is controlled in accordance with the detected pressure value. An electric vacuum cleaner using such a technique is disclosed, for example, in Japanese Patent Laying-Open No. 57-75623 (1982).
In such a conventional technique, however, input to the electric blower was controlled merely in accordance with detection of the pressure in the dust collecting chamber, and it was difficult to perform optimum input control adapted to the actual condition of the floor surface which is subject to dust collection.
For example, on of the surface of a board floor, the suction port of the electric vacuum cleaner tends to cling to the floor surface, and once it clings to the floor, the pressure in the air inlet passage is lowered. In such a case, input to the electric blower is increased in accordance with the decrease of detected output of the pressure detecting device to make the suction power still greater, so that the suction port clings to the floor surface still harder. As described above, there was a problem in the conventional electric vacuum cleaner, in that input control of the electric blower adapted to the actual condition of the floor surface was not performed, and convenience of use was not sufficiently improved.
Another approach is disclosed in Japanese Patent Laying-Open No. 64-52430 (1989), for example, in which suction power in accordance with the type of a floor surface is realized by sensing the change in electric current in a driving motor of a dust collecting rotary brush provided in a suction element of the vacuum cleaner and automatically controlling input to an electric blower on the basis of the sensed output. However, during normal cleaning, the change in current in the motor driving the rotary brush is extremely small, and, particularly, little change occurs in the average current. Therefore, it is difficult to perform fine input control of the electric blower in accordance with the type or the condition of the floor merely by controlling input to the electric blower in proportion to the current in the driving motor of the rotary brush as in the above described conventional technique.